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Shenoy" , "Mario Limonciello" , Perry Yuan , , , , , "Shyam Sundar S K" , Perry Yuan Subject: [PATCH v4 01/13] Documentation: x86: Add AMD Hardware Feedback Interface documentation Date: Mon, 21 Oct 2024 13:02:40 -0500 Message-ID: <20241021180252.3531-2-mario.limonciello@amd.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20241021180252.3531-1-mario.limonciello@amd.com> References: <20241021180252.3531-1-mario.limonciello@amd.com> Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: SATLEXMB04.amd.com (10.181.40.145) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PEPF000023D0:EE_|LV8PR12MB9262:EE_ X-MS-Office365-Filtering-Correlation-Id: 05f616d1-eb09-4a9a-ff93-08dcf1faa421 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; ARA:13230040|82310400026|376014|1800799024|36860700013; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17; CTRY:US; LANG:en; SCL:1; SRV:; IPV:CAL; SFV:NSPM; H:SATLEXMB04.amd.com; PTR:InfoDomainNonexistent; CAT:NONE; SFS:(13230040)(82310400026)(376014)(1800799024)(36860700013); DIR:OUT; SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Oct 2024 18:03:17.6171 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 05f616d1-eb09-4a9a-ff93-08dcf1faa421 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d; Ip=[165.204.84.17]; Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SJ1PEPF000023D0.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: LV8PR12MB9262 From: Perry Yuan Introduce a new documentation file, `amd_hfi.rst`, which delves into the implementation details of the AMD Hardware Feedback Interface and its associated driver, `amd_hfi`. This documentation describes how the driver provides hint to the OS scheduling which depends on the capability of core performance and efficiency ranking data. This documentation describes * The design of the driver * How the driver provides hints to the OS scheduling * How the driver interfaces with the kernel for efficiency ranking data. Signed-off-by: Perry Yuan Reviewed-by: Mario Limonciello Signed-off-by: Mario Limonciello --- v3->v4: * Add another sentence to classifications (Ricardo) v2->v3: * Rewording (Bagas) * Fix toctree entry name (Bagas) --- Documentation/arch/x86/amd-hfi.rst | 129 +++++++++++++++++++++++++++++ Documentation/arch/x86/index.rst | 1 + 2 files changed, 130 insertions(+) create mode 100644 Documentation/arch/x86/amd-hfi.rst diff --git a/Documentation/arch/x86/amd-hfi.rst b/Documentation/arch/x86/amd-hfi.rst new file mode 100644 index 0000000000000..b66ff083855f3 --- /dev/null +++ b/Documentation/arch/x86/amd-hfi.rst @@ -0,0 +1,129 @@ +.. SPDX-License-Identifier: GPL-2.0 + +====================================================================== +Hardware Feedback Interface For Hetero Core Scheduling On AMD Platform +====================================================================== + +:Copyright: 2024 Advanced Micro Devices, Inc. All Rights Reserved. + +:Author: Perry Yuan +:Author: Mario Limonciello + +Overview +-------- + +AMD Heterogeneous Core implementations are comprised of more than one +architectural class and CPUs are comprised of cores of various efficiency and +power capabilities: performance-oriented *classic cores* and power-efficient +*dense cores*. As such, power management strategies must be designed to +accommodate the complexities introduced by incorporating different core types. +Heterogeneous systems can also extend to more than two architectural classes as +well. The purpose of the scheduling feedback mechanism is to provide +information to the operating system scheduler in real time such that the +scheduler can direct threads to the optimal core. + +The goal of AMD's heterogeneous architecture is to attain power benefit by sending +background thread to the dense cores while sending high priority threads to the classic +cores. From a performance perspective, sending background threads to dense cores can free +up power headroom and allow the classic cores to optimally service demanding threads. +Furthermore, the area optimized nature of the dense cores allows for an increasing +number of physical cores. This improved core density will have positive multithreaded +performance impact. + +AMD Heterogeneous Core Driver +----------------------------- + +The ``amd_hfi`` driver delivers the operating system a performance and energy efficiency +capability data for each CPU in the system. The scheduler can use the ranking data +from the HFI driver to make task placement decisions. + +Thread Classification and Ranking Table Interaction +---------------------------------------------------- + +The thread classification is used to select into a ranking table that describes +an efficiency and performance ranking for each classification. + +Threads are classified during runtime into enumerated classes. The classes represent +thread performance/power characteristics that may benefit from special scheduling behaviors. +The below table depicts an example of thread classification and a preference where a given thread +should be scheduled based on its thread class. The real time thread classification is consumed +by the operating system and is used to inform the scheduler of where the thread should be placed. + +Thread Classification Example Table +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ++----------+----------------+-------------------------------+---------------------+---------+ +| class ID | Classification | Preferred scheduling behavior | Preemption priority | Counter | ++----------+----------------+-------------------------------+---------------------+---------+ +| 0 | Default | Performant | Highest | | ++----------+----------------+-------------------------------+---------------------+---------+ +| 1 | Non-scalable | Efficient | Lowest | PMCx1A1 | ++----------+----------------+-------------------------------+---------------------+---------+ +| 2 | I/O bound | Efficient | Lowest | PMCx044 | ++----------+----------------+-------------------------------+---------------------+---------+ + +Thread classification is performed by the hardware each time that the thread is switched out. +Threads that don't meet any hardware specified criteria will be classified as "default". + +AMD Hardware Feedback Interface +-------------------------------- + +The Hardware Feedback Interface provides to the operating system information +about the performance and energy efficiency of each CPU in the system. Each +capability is given as a unit-less quantity in the range [0-255]. A higher +performance value indicates higher performance capability, and a higher +efficiency value indicates more efficiency. Energy efficiency and performance +are reported in separate capabilities in the shared memory based ranking table. + +These capabilities may change at runtime as a result of changes in the +operating conditions of the system or the action of external factors. +Power Management FW is responsible for detecting events that would require +a reordering of the performance and efficiency ranking. Table updates would +happen relatively infrequently and occur on the time scale of seconds or more. + +The following events trigger a table update: + * Thermal Stress Events + * Silent Compute + * Extreme Low Battery Scenarios + +The kernel or a userspace policy daemon can use these capabilities to modify +task placement decisions. For instance, if either the performance or energy +capabilities of a given logical processor becomes zero, it is an indication that +the hardware recommends to the operating system to not schedule any tasks on +that processor for performance or energy efficiency reasons, respectively. + +Implementation details for Linux +-------------------------------- + +The implementation of threads scheduling consists of the following steps: + +1. A thread is spawned and scheduled to the ideal core using the default + heterogeneous scheduling policy. +2. The processor profiles thread execution and assigns an enumerated classification ID. + This classification is communicated to the OS via logical processor scope MSR. +3. During the thread context switch out the operating system consumes the workload(WL) + classification which resides in a logical processor scope MSR. +4. The OS triggers the hardware to clear its history by writing to an MSR, + after consuming the WL classification and before switching in the new thread. +5. If due to the classification, ranking table, and processor availability, + the thread is not on its ideal processor, the OS will then consider scheduling + the thread on its ideal processor (if available). + +Ranking Table +------------- +The ranking table is a shared memory region that is used to communicate the +performance and energy efficiency capabilities of each CPU in the system. + +The ranking table design includes rankings for each APIC ID in the system and +rankings both for performance and efficiency for each workload classification. + +.. kernel-doc:: drivers/platform/x86/amd/hfi/hfi.c + :doc: amd_shmem_info + +Ranking Table update +--------------------------- +The power management firmware issues an platform interrupt after updating the ranking +table and is ready for the operating system to consume it. CPUs receive such interrupt +and read new ranking table from shared memory which PCCT table has provided, then +``amd_hfi`` driver parse the new table to provide new consume data for scheduling decisions. + + diff --git a/Documentation/arch/x86/index.rst b/Documentation/arch/x86/index.rst index 8ac64d7de4dc9..56f2923f52597 100644 --- a/Documentation/arch/x86/index.rst +++ b/Documentation/arch/x86/index.rst @@ -43,3 +43,4 @@ x86-specific Documentation features elf_auxvec xstate + amd-hfi